Common side effects of glucosamine include heartburn, diarrhea, upset stomach, nausea and constipation, as listed by Arthritis Foundation. It can also raise blood pressure, blood glucose levels, triglyceride levels and cholesterol, and it may increase eye pressure in persons with intraocular hypertension or glaucoma.
Dividing a daily dose of glucosamine into two or three doses over the course of the day helps prevent stomach upset, as stated by Arthritis Foundation. Although many glucosamine supplements are made from shellfish such as crab and lobster, others are derived from vegetable sources, making them suitable for individuals with shellfish allergies. If an allergic reaction does occur, symptoms can be severe and may include hives, chest tightness, difficulty breathing, facial swelling and itching, according to Drugs.com. Call a doctor immediately if any of these symptoms appear after taking glucosamine.
Pregnant women, breast-feeding women and children should not take glucosamine, and diabetic patients should consult a doctor before taking the supplement due to its effect on blood sugar, as instructed by Drugs.com. The long-term safety and effects of glucosamine are still unknown as of 2015. Persons who have allergies, are taking arthritis medicine or are taking any other prescription or over-the-counter medications should speak with a doctor before taking glucosamine.